'X Factor': Alex and Sierra on 'Say Something' and singing Destiny's Child in front of Kelly Rowland

alex-and-sierra-say-something-destinys-child-say-my-name.jpgAfter weeks and weeks of "The X Factor" live shows -- and weeks and weeks of critiques from the four judges -- Alex and Sierra finally have tough enough skin that the criticisms don't affect them as much.

"I think I have just gotten to the point where I really want good comments from them but I'm kind of like whatever happens happens and I'm gonna just not care what anyone says even though I really do care," Sierra tells Zap2it backstage after her performance on the Top 6 live show. Adds Alex, "She's convinced herself that she doesn't care. ... It's fun watching her be this Sierra, because this is the Sierra I've always known. It's fun to see her not afraid of what someone's going to say to her. She's just doing what she does and leaving it all up there."

Luckily, though, their feedback was universally positive -- probably because they absolutely destroyed (in the good way) both songs they took on this week, "Say My Name" and "Say Something." They were mighty nervous to take on Destiny's Child with one of the original members sitting in front of them, but it worked out just fine. "That was pretty nerve-wracking," says Sierra. "It wasn't like it was a group we weren't around to hear and we were just doing it. That's one of the groups I listened to constantly growing up and to sing it for Kelly [Rowland] -- all we wanted was just like 'That was good.'"

Instead, Rowland loved their version of her hit. She also loved their second song, a version of Great Big World and Christina Aguilera's "Say Something." It was a gorgeous rendition of a somber song, so it's interesting to note that the music playing in the studio beforehand was Michael Jackson's "Beat It," which inspired Alex to bust out a moonwalk before the commercial break ended. "Oh, you saw that? Yikes," Alex says of his impromptu dance recital. "Well, they were playing Michael Jackson and that's the only dance move that I can kind of almost do a little bit. Other than the robot. I'm a really bad dancer. It was probably a weird time to do it, right before we do the most depressing song of all time. Gotta get all the happy out."

Though having the stripped-down songs later in the show meant the energy level in the studio dropped a bit, Sierra says it was better that way. "We wanted the unplugged later. It was easier to get the fun one done and then take it down rather than, like, cry and then have to be like 'Say My Name!'"

It worked, because it felt like they were playing for themselves rather than a TV audience of millions. "I think we really wanted to make it intimate. We sang it to each other," says Alex.

Here's something you didn't know about their performances this week: Sierra is super sick. "I can say it now since we've already performed and it's not an excuse -- I'm really sick. I got one of those shots in my bum," she says. Adds Alex, "That's why she's talking at 7 million miles per hour!" Luckily, Mario Lopez didn't bring it up during the broadcast. "I was afraid they would be like, 'Are you sick?' and I didn't want to use it as an excuse," says Sierra.

UPDATE: A day later, and Alex and Sierra's version of "Say Something" is No. 1 on iTunes and holding strong. "It's crazy," Alex tells Mario Lopez during the Top 6 results show.
Photo/Video credit: FOX